In my Italian Pat. No. 962,067 I have disclosed a dual horn with a pair of convoluted wind channels separated by a curved partition, i.e. a longer outer channel and a shorter inner channel, terminating in a common bell-shaped outlet. Upon the admission of air under pressure to the entrance ends of the two wind channels remote from the bell, sounds of higher and lower pitch are respectively generated in the inner and in the outer channel as an acoustic signal.